Atomic theory describe:

a. the parts that make up an atom.
b. why a microscope make something look bigger.
c. how to make a solution from two liquids.
d. how to calculate the speed of light.

The correct option is A. Atomic theory describes the parts that make up an atom.

Explanation:

In ancient times, atoms were known to be the smallest particles present in a substance. Over time, researches made by scientists showed that an atom even has smaller parts which are termed as subatomic particles. The most widely accepted atomic theory explains that all matter present in the universe is made up of atoms. The nucleus is the neutral sub-atomic part of an atom, Proton is the positive charge carrier of an atom. The nucleus and protons are present inside the nucleus of the atom. The electrons are the negative part which revolves in orbits around the nucleus.